Preparation of decarbonylation products of carboxylic acids



United States Patent C ABSTRACT OF THE DISCLOSURE The process for the decarbonylation of alpha-hydroxylamino-carboxylic acids is disclosed. Alpha-hydroxylamino-carboxylic acids are treated with a strong acid to form a nitrogenous product, which may be an oxime, an amide or a lactam.

The present invention relates to the preparation of decarbonylation products of carboxylic acids substituted at the alpha-carbon atom. More particularly, the present invention relates to the preparation of decarbonylation products of alpha-hydroxylamino-carboxylic caids.

In a known method of preparing aldehydes, alpha-hydroxy-carboxylic acids are treated with a strong acid, whereby carbon monoxide and water are split off, so that an aldehyde is obtained. In the same manner, an alphahydroxy-carboxylic acid whose alpha-carbon atom is not bound to a hydrogen atom, but attached to an alkyl or aryl group can be used to prepare the corresponding ketone.

It has now been found that the decarbonylation process can be applied to alpha-hydroxylamino-carboxylic acids to produce valuable decarbonylation products.

A process has now been found in which decarbonylation of alpha-hydroxylamino-carboxylic acids is carried out with a strong acid, whereby the corresponding lactam or other material is obtained, with the splitting off of carbon monoxide from the carboxylic acids. Generally, a nitrogen-contaning product is obtained, e.g., oximes, amides and lactams.

Examples of alpha-hydroxylamino-carboxylic acids which may be used are the normal or branched alphahydroxylamino-alkane carboxylic acids, e.g., alpha-hydroxylamino-n-valeric acid, alpha hydroXylamiuo-ncaproic acid, and alpha-hydroxylamino-isobutyric acid; and alpha-hydroxylamino-cyclo-alkane carboxylic acids, e.g., alpha-hydroxylamino-cyclohexane carboxylic acid and alpha-hydroxylamino-cycloheptane carboxylic acid. The alpha-hydroxylamino-carboxylic acids which can be employed in the process of the present invention contain at least 2 carbon atoms and preferably contain from 2 to 13 carbon atoms.

The decarbonylation according to the invention is carried out by means of a strong acid, e.g., phosphoric acid, polyphosphoric acid, hydrochloric acid, sulfuric acid and oleum, or a mixture of liquid sulfur dioxide and sulfur trioxide.

The amount of strong acid which should be used in the reaction mixture can be varied within wide limits. In general, we prefer to use an amount of strong acid corresponding to at least about 4 moles of acid to one mole of alpha-hydroxylamino-carboxylic acid in the reaction mixture.

The reaction can be carried out at atmospheric pressure and it is not necessary to apply a higher or a lower pressure. Therefore, the reaction can be carried out by the use of simple apparatus.

Patented Feb. 13, 1968 The temperature at which the decarbonylation is carried out can be varied within wide limits. It is not necessary to use very high temperatures, e.g., above 250 C., as in most cases the process can be realized at room temperature or low temperature, e.g., 10 to 30 C. If the reaction is carried out in the presence of sulfur trioxide, spontaneous evolution of gas will occur at this low temperature, as a result of carbon monoxide being split off. This gas evolution is promoted if stirring takes place.

In choosing the reaction temperature, the nature of the alpha-hydroxylamino-carboxylic acid used as the starting product and the nature of the decar-bonylation products desired should be taken into consideration. If, for instance, the starting product is alpha-hydroxylamino-isobutyric acid, mainly acetone oxime will be formed at a relatively low temperature of 10-25 C., while mainly N-methylacetamide will be obtained at a relatively high temperature of -150 C.

If the process is started fromalpha-hydroxylamino-cycloalkane carboxylic acids, the decarbonylation will yield w-lactams.

Unless otherwise specifically stated, all parts and percentages are by weight.

Example I In a 5-liter reaction vessel equipped with a stirrer, 150 g. of alpha-hydroxylamino-cyclohexane carboxylic acid is dissolved in 500 ml. of sulfuric acid (concentration 96% by weight). While the solution is being stirred, 500 ml. of oleum (sulfur trioxide content 20% by weight) is slowly added over a period of 0.5 hr., at a temperature of 20 C., and after this addition stirring is continued for one more hour at the same temperature.

When the oleum is added, gas evolution starts to take place. The carbon monoxide leaving the reaction mixture is collected and measured. The amount of carbon monoxide thus collected corresponds to the theoretical amount.

Thereafter, the reaction mixture is chilled by pouring onto 5 kg. of crushed ice. Then suflicient amount of ammonia is added to neutralize the reaction mixture to a pH value of 7.

After extraction with chloroform and removal of the solvent, 104 g. of e-caprolactam is obtained (yield 98%) Example II The decarbonylation of 208 g. of alpha-hydroxylamino-cycloheptane carboxylic acid is carried out in a similar way as described in Example I.

In this case the amount of carbon monoxide collected is also the theoretical amount.

4'he process yields 144 g. of w-oenant'holactam (yield 9 0).

Example III In a 10-liter reaction vessel provided with a stirrer, 795 g. of alpha-hydroxylamino-cyclohexane carboxylic acid is dissolved in 5 liters of polyphosphoric acid (phosphorus pentoxide content 82% by weight). While being stirred, the solution is heated to C. in 0.5 hr., after which stirring is continued at this temperature for 1.5 hours.

Thereafter the reaction mixture is chilled by pouring onto 10 kg. of ice, and the process is continued as described in Example I.

The amount of carbon monoxide collected is 63% of the theoretical amount, and the amount of E-caprolactam obtained is 365 g. (yield 100% at this degree of conversron Example IV In the apparatus described in Example III, 1330 g. of alpha-hydroxylamino-n-valeric acid is dissolved in 2.5

liters of sulfuric acid (100%). While the solution is being stirred, 2.5 liters of oleum (sulfur trioxide content 20% by weight) is slowly added over a period of 1 hour, at a temperature of 20-40 C. During the addition of the oleum gas is slowly evolved. Stirring is continued at 2040 C., until after 10 hours, the evolution of gas has stopped. Then the reaction mixture is subjected to further treatment as described in Example I. p

The amount of carbon monoxide collected is 99% of the theoretical amount, and the amount of butyramide obtained is 700 g. (yield 81%).

Example V In the apparatus described in Example III, 1071 g. of alpha-hydroxylamino-isobutyric acid is dissolved in 2.5 liters of sulfuric acid (100%). While the solution is being stirred, 2.5 liters of oleum (sulfur trioxide content 20%) is slowly added over a period of 1 hour, at a temperature of 15-20 C.; during this addition, gas is evolved. Stirring in continued at the said temperature for another 2 hours, and the reaction mixture is then subjected to further treatment as described in Example I.

The amount of carbon monoxide collected is 80% of the theoretical amount, and acetoxime is obtained in an amount of 280 g. (yield 52% at this degree of conversion).

Example VI The decarbonylation described in Example V is repeated at a higher temperature. In this process 685 g. of alpha-hydroxylamino-isobutyric acid is dissolved in 1.6 liters of sulfuric acid (100%), and the solution is slowly heated in 1 hour to a temperature of 120 C. During this heating, a slow evolution of gas took place.

Subsequently, while the solution is being stirred, 2.2 liters of oleum (sulfur trioxide content 20% by weight) is slowly added over a period of 1 hour, during this addition the temperature is increased to 140 C. The reaction mixture is then subjected to further treatment as described in Example I.

The amount of carbon monoxide collected is 81% of the theoretical amount,- and in this process 334 g. of N-methyl-acetamide is obtained (yield 99% of this degree of conversion).

What is claimed is:

1. The process for the decarhonylation of alpha-hydroxylamino-carboxylic acids which comprises treating an alpha-hydroxylarnino-carboxylic acid selected from the group consisting of normal alpha-hydroxylaminoalkane carboxylic acids containing from 2 to about 13 carbon atoms, branched-chain alpha-hydroxylamino-alkane carboxylic acids containing from 2 to about 13 carbon atoms, and alpha-hydroxylamino-cycloalkane carboxylic acids containing from about to about 13 carbon atoms, with a strong acid selected from the group consisting of phosphoric acid, polyphosphoric acid, hydrochloric acid, sulfuric acid and oleum, and a mixture of sulfur dioxide and sulfur trioxide, to form a nitrogencontaining product selected from the group consisting of oximes, amides and lactams.

2. The process for preparing N-methyl-acetamide comprising:

dissolving alpha-hydroxylamino-isobutyric acid in sulfuric acid,

heating the mixture to a temperature of from about 120 to about 125 C.,

5 adding at least 2 moles of oleum per mole of alphahydroxylamino-isobutyric acid dissolved in said mixture,

and heating the resultant mixture to a temperature of from about 125 to about 150 C. to produce the N-methyl-acetamide. 3. The process for preparing acetoxime comprising: dissolving alpha-hydroxylamino-isohutyric acid in sulfuric acid, maintaining the mixture at a temperature of from about to about 25 C., and adding at least 2 moles of oleum per mole of alphahydroxylamino-isobutyric acid dissolved in said mixture to produce the acetoxime. 4. The process for preparing butyramide comprising: dissolving alpha-hydroxylamino-n-valeric acid in sulfuric acid, maintaining the mixture at a temperature of from about i 10 to about 150 C.,

and adding at least 2 moles of oleum per mole of alpha hydroxylamino-n-valeric' acid dissolved in said mixture to produce the butyramide. 5. The process for preparing omega-oenantholactam comprising:

dissolving alpha-hydroxylamino-cycloheptane carboxylic acid in sulfuric acid, maintaining the mixture at a temperature of from about 10 to about 150 C., and adding at least 2 moles of oleum per mole of alphahydroxylamino-cycloheptane carboxylic acid dissolved in said mixture to produce the omega-oenantholactam. 6. The process for preparing e-caprolactam comprismg:

dissolving alpha hydroxylamino cyclohexane carboxylic acid in sulfuric acid, maintaining the mixture at a temperature of from about 10 to about 150 C., and adding at least 2 moles of oleum per mole of alphahydroxylamino-cyclohexane carboxylic acid dissolved in said mixture to produce the e-caprolactam. 7. The process for preparing e-caprolactam comprismg:

dissolving alpha-hydroxylamino-cyclohexane carboxylic acid in polyphosphoric acid,

and heating the mixture to a temperature of from about 50 to 150 C. to produce the e-caprolaetam.

References Cited UNITED STATES PATENTS 3,022,291 2/ 1962 Muench et al 260-2393 JOHN D. RANDOLPH, Primary Examiner.

WALTER A. MODANCE, Examiner. R. BOND, Assistant Examiner. 

